The present invention relates to an electrically heatable sheet of glass which has an electrically conductive coating on the surface of the sheet of glass and also to a special contacting of this electrically conductive coating. Furthermore, the present invention relates to a method for the production of this sheet of glass and also a window which includes the sheet of glass according to the invention. Likewise, possibilities for using the sheet of glass are indicated.
Electrically conductive and extensively transparent coated glasses and plastic material films have attained a wide field of application industrially. The functions of such substrates with electrically conductive transparent thin layers extend from the cover electrode in liquid crystal display elements, so-called liquid crystal displays (LCDs), via thin film transistor (TFT) displays, via cover electrodes for electroluminescent displays, computer screen elements as far as electrostatic screening elements, heating elements for mirrors and burglar alarm glazing and the like.
The production of such electrically conductive and extensively transparent inorganic thin films can thereby be effected in sputtering technology or vapour deposition technology and also pyrolytically with a subsequent temperature treatment in the range of 450 to 750° C. The thermoplastic films or sheets are coated for example by means of low temperature sputtering and deposition technologies. Likewise, indium-tin oxide (ITO) or tin oxide (NESA) pastes and similar metal oxides which are embedded in a corresponding polymer matrix or pastes with intrinsically conductive polymers, electroactive polymer films, such as polyanilines, polythiophenes, polyacetylenes, polypyrrols (Handbook of Conducting Polymers, 1986) and such polymers with and without metal oxide filling are used. These are applied by means of screen printing, knife-coating, spraying, painting and similar application techniques, substantial achievements in drying at low temperatures of for example 80 to 120° C. having been made and also in the high elasticity in the case of deformation and of course in the case of as high transparency as possible with low surface resistance.
A special type of electrically conductive and highly transparent float glass is represented by the pyrolytically produced layers which have high surface hardness and the electrical surface resistance of which can be adjusted within a very wide range of typically a few milliohms up to 3,000 ohms per square with a daylight transparency of typically 77 to 86%. There may be mentioned here by way of example TEC glass by the company Pilkington Libbey-Owens-Ford, Toledo Ohio, USA. Glass with the name TEC 15/4 has 4 mm glass thickness and offers a surface resistance of less than 14 ohms per square with a daylight transparency of 83%. Glass with the name TEC 70/4 likewise has 4 mm glass thickness and offers a surface resistance of less than 80 ohms per square with a daylight transparency of 82%. Such glasses can be readily shaped and have good scratch resistance. In particular, scratches do not lead to an electrical interruption of the electrically conducting surface layer but merely to a generally slight increase in surface resistance. In the case of purely surface layers, such as an ITO sputtered layer or vapour deposited layer, damage to the surface, such as for example scratches or cracks due to thermal surface tensions, lead to an interruption in the electrical surface conductivity and hence to failure of the system. Furthermore, pyrolytically produced conductive surface layers are diffused and anchored strongly in the surface by their temperature treatment such that, with a subsequent material application, an extremely high adhesive bond to the glass substrate is provided, which is likewise very advantageous for the present invention. In addition, such coatings have good homogeneity, i.e. a low dispersion of the surface resistance value over large surfaces and this property likewise represents an advantage for the present development.
The use of such K glasses as electrical heating element for example mirror heating and the like is likewise already known.
In WO 01/10790, a glass article for use in building technology for reducing heating due to solar radiation is described. In this invention, a coating of a glass substrate based on antimony-doped tin oxide layers in combination with fluorine-doped tin oxide layers is mentioned such that high light permeability of visible light is achieved therefrom and, at the same time, low permeability by sunlight is provided.
In WO 00/53062, a window element for a display case is described, which is formed from a tempered glass plate which has a transparent and electrically conductive coating and a pair of electrically conductive bus bars on at least one side, the conductive coating being able to be heated. In a further embodiment, a spaced two-sheet window element is described; the inside of the outer sheet of glass or the outside of the inner sheet of glass is thereby heated. Furthermore, it is explained that the electrically conductive coating is formed from the group consisting of tin oxide, indium-tin oxide, zinc oxide and cadmium stannate, it has a thickness of 50 to 900 nanometers and each individual bus bar of the pair of bus bars comprises electrically conductive material which is chosen from the group silver, silver alloy, copper and copper alloy. Application of the pair-wise bus bar contact strips is effected before application of the electrically conductive transparent layer. After application of the pair-wise bus bar contact strips and subsequent to the electrically conductive coating, the sheets of glass are bent to the desired contour and tempered in the glass melting furnace. The lateral spacing and sealing elements are described in detail in a further patent specification U.S. Pat. No. 5,622,414.
In EP 0 300 300 B1, a method for applying a coloured coating on a surface of a sheet of glass by means of a screen printing technique and using pasty to free-flowing mixed coating mixtures from layer silicates, oxides, metal modifications and carbon modifications with a binder solution based on phosphate and hence to a glass frit-free coating mixture is described and, applied in such a manner on the glass surface, is burnt in at temperatures in the range of between 550 to 700° C. In a special embodiment, the coating mixture is adjusted to be conductive by adding carbon black by up to 10 parts by weight and sheets of glass treated in this way offer good resistance to breakage, good adhesion- and scratch resistance, and also good corrosion resistance and good suitability for composite glass safety sheets.
In WO 93/26138 and WO 94/00044, a radiant heating panel and electrically heatable tableware and corresponding production methods were described. Underlying both inventions is a so-called electric-arc spraying process in the form of flame spraying or plasma spraying.
In U.S. Pat. No. 5,080,146, an improved and cost-saving method for filling units of composite sheets of glass with a low-conductive gas, such as the relatively expensive krypton or also with argon, xenon, CO2, air, SF6 and fluorocarbon gas, is described. In this invention, the seal at the glass edges is furthermore described and seals based on silicones, butyl rubber, polyurethanes or polysulphides are mentioned and a gas loss of composite sheets of glass sealed in this manner of less than 1% over very long periods of time is indicated.
In EP 0 394 089 B1, an electrically heatable car sheet of glass with an electrically conductive, transparent surface coating serving as heat resistance, with current supply conductors disposed along two oppositely situated sheet edges and with a frame-like decorative layer made of an opaque and electrically conductive colour, in particular a burnt-in colour, is described. The two current supply conductors are in electrically conducting contact with the surface coating and consist of metal foil strips or metal bands which are in electrical contact with the decorative layer in the region of the frame-shaped decorative layer. In this invention, absolutely no electric-arc spraying processes for production of contact strips are mentioned either.
In EP 0 397 292 B1, a method for the production of a thin transparent and electrically conducting layer made of metal oxide(s) on a substrate, in particular on glass, is mentioned. This is achieved by spraying on metal compounds made of indium formiate and for example dibutyltin oxide and/or dibutyltin difluoride as a powder in suspension in a carrier gas onto the substrate brought to an increased temperature, which metal compounds decompose in contact with the substrate and, with formation of the metallic oxide layer, oxidise or the powder in contact with the substrate being pyrolised with formation of a thin layer based on indium oxide.